What Are Bivalves? - Definition, Characteristics & Examples

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  • 0:00 What is a Bivalve?
  • 1:00 Characteristics of Bivalves
  • 2:39 Examples of Bivalves
  • 4:19 Lesson Summary
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Lesson Transcript
Instructor: Heather Pier

Heather has taught high school and college science courses, and has a master's degree in geography-climatology.

Expand your knowledge of the animal kingdom by learning about bivalves, a type of shelled animal that can be found all over the world in different water environments. Then test yourself on your new knowledge.

What Is a Bivalve?

You may have seen or even eaten an oyster or scallop. You likely know them as shellfish. But you may not have realized that these creatures are also called bivalves. A bivalve is an animal belonging to the class Bivalvia. The word 'bivalve' comes from the Latin bis ('two') and valvae ('leaves of a door'). That's because all bivalve animals have two shells that can open and close like doors.

Bivalves are aquatic animals, and different species of bivalves can be found in freshwater, saltwater and even brackish, slightly salty, water environments. They typically live on the seafloor, on seabeds or attach themselves to the sides of hard surfaces, like rocks or manmade pipes.

These animals are abundant throughout the world, and because of their wide availability, they are a very commonly consumed form of seafood.

Characteristics of Bivalves

The most important feature of a bivalve is its two shells, called valves. These shells act like a protective armor, guarding the bivalve's soft inner body parts. They can open their shells to move and feed, but at the first hint of a threat, they will rapidly close their shells.

The muscle that helps them to close their valves is called the foot. This foot isn't like a human foot. Instead, it is a large muscle that joins the two valves together and helps to open and close them. In that respect, the foot moves much more like one of your hinged joints, like your knee or elbow.

Another feature of bivalves is that, unlike many animals, they don't have mouths and teeth with which to eat. Instead, they have a tube-like body part called a siphon that takes in microscopic particles of food dissolved in the water. The food goes then into the stomach for processing, and any oxygen in the water is passed along to their gills, which function similar to fish gills, for respiration.

Any waste products and gases, like carbon dioxide, are also passed out of the body using a different siphon. The siphon that takes in nutrients is often called the in-current siphon, whereas the wastes exit through the out-current siphon.

It's also worth noting that bivalves typically don't have eyes. Some have a few primitive eyes, but most do not. Considering that they often live in dirty, cloudy water, which has more particles for them to feed on, they probably wouldn't be able to see most of the time anyway.

Examples of Bivalves

There are many species of bivalves, both currently living and fossilized. We've mentioned that oysters and scallops are examples of bivalves, but so are clams and mussels. These are the most common bivalves living today.

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